The present invention relates to the field of three-dimensional prototype modeling. In particular, the present invention is a rapid prototyping system for forming three-dimensional objects of predetermined design by depositing multiple layers of a material in its fluid state from an extrusion head onto a base. The material is selected and its temperature is controlled so that it solidifies upon extrusion or dispensing onto the base, with the build-up of the multiple layers forming the desired object. In the present invention, three-dimensional objects are formed on a flexible substrate which is held in position by a vacuum platen.
A rapid prototyping system evolves the making of three-dimensional objects based upon design data which is provided from a computer aided design (CAD) system. Examples of apparatus and methods for rapid prototyping of three-dimensional objects by depositing layers of solidifying material are described in Crump U.S. Pat. No. 5,121,329, Batchelder et al. U.S. Pat. No. 5,303,141, Crump U.S. Pat. No. 5,340,433, Batchelder U.S. Pat. No. 5,402,351, Batchelder U.S. Pat. No. 5,426,722, Crump et al. U.S. Pat. No. 5,503,785, and Abrams et al. U.S. Pat. No. 5,587,913, all of which are assigned to Stratasys, Inc.
In a rapid prototyping system of the type described in the aforementioned patents, the material being deposited must adhere to removable base member or substrate to form a foundation layer over which the remaining layers of the object are deposited, one layer at a time. It is preferred that parts deposited on the removable substrate be strongly adhered thereto to overcome two effects. First, strains generated within the extruded material tend to warp the deposited structures unless the structures are supported in their correct orientation. The substrate is important in serving to avoid localized shrinkage in the foundation layer. Second, there are forces from the deposition process itself, such as pull from the nozzle and centripetal acceleration on parts that are not stationary, that tend to distort the deposited structures. A delamination of the foundation layer from the substrate during the building of the object could result in a total failure in forming the object. Further, since the removable substrate becomes a defining surface for the parts being built, it must be held in a well-defined configuration approximating a plane.
After the object has been formed, it must be separated from the substrate without damage to the object. Therefore, after the deposition process, it is preferred that the parts deposited on the substrate be weakly adhered thereto in order that the parts might be removed from the extrusion apparatus without damage.
The Crump U.S. Pat. Nos. 5,121,329 and 5,340,433 teach the use of a fine wire mesh screen coated with sand as the substrate. The "sandpaper" can be applied to the base plate by double-faced adhesive tape. Separation of the object from this "sandpaper" substrate can be facilitated by applying a low voltage current to the wire mesh screen after the object is formed. The patents also suggest, as an alternative, a substrate made of water soluble wax which could be dissolved to separate the object from the substrate without damage. A third suggested alternative base member for receiving the foundation layer is a foam plastic material. The coarse, porous structure of a blue polystyrene material manufactured by Dow-Corning Corp. under that name is identified as particulary suitable.
A substrate may also be pre-coated with a thermoplastic adhesive that melts at a lower temperature than the deposited material, and heater elements mounted in a build platform to allow adhesive of the substrate to the base during the build process, and removal by heating the adhesive thereafter.
In rapid prototyping systems sold in the past by Stratasys, Inc., a preferred substrate material has been a polymer foam, which can be broken away from the object once it has been formed. The foam is removably mounted to a platform by spears that engage from the foam from all sides. While foam substrates have found substantial use, they have a number of disadvantages. First, it is difficult to maintain a perfectly flat substrate surface when a foam substrate is used, particularly when large objects are to be formed which require a large substrate. Second, foam substrates at times can be difficult to remove from the completed prototype objects. Third, removal of foam substrates produces dust.